During the last decade or so, the familiar automobile storage battery has undergone several major improvements. In particular, the placement of the battery terminals has been shifted in some cases from the top of the battery container to the sidewalls thereof.
A great deal of research effort has been expended in order to eliminate or at least substantially reduce battery terminal corrosion. Conventional top terminals are constantly exposed to the debilitating effects of the environment. Rain, road splash, road salt, and airborne pollutants in combination with the electrolyte of the battery all eventually take their corrosive toll of the battery terminals. As the familiar white powdery corrosion products collect (primarily lead sulfate and lead carbonate), the electrical contact between the battery terminals and the cable connectors inexorably deteriorates thereby reducing the effectiveness of the battery. Furthermore, the corrosive materials also serve as ionic short circuit paths between the terminals. As a result, these corrosive products tend to reduce the capacity and cranking ability of the battery and, more importantly, shorten its life.
Accordingly, by recessing the terminals within the battery walls, the terminals may be protected from the more deleterious effects of the environment. Moreover, by virtue of the side terminal design, appreciable savings involving the quantity of lead utilized in the construction of the battery may be realized. Instead of employing a relatively long vertical lead riser to make contact with a terminal disposed in the battery cover, a substantially shorter riser may be used to make contact with a terminal disposed within an adjacent wall.
A common sidewall terminal configuration presently in use has a terminal plug passing through an aperture formed within the battery case wall. In some cases, the terminal plug is injection molded about the container. Regardless of the method employed, the back end of the plug is usually either flush with the inner wall of the container or it actually extends into the battery compartment itself. A riser is then welded or torch burned to the back end. Sometimes, an additional slab of lead is interposed between the riser and the back end of the plug. Representative designs are shown in U.S. Pat. Nos. 3,775,730, 4,143,215, 4,166,155, 3,767,407, 4,150,202 and 3,843,411.
Unfortunately, in attaining lead economy and terminal protection, a new problem arises with side terminal designs. By conscious choice, a side terminal is usually disposed at or below the electrolyte level of the battery. Sulfuric acid, with its well known propensity for creeping through the smallest of voids, will often leak out of the battery around the terminals.
In a nutshell, the leaking problem is engendered by the combination of a welded metallic terminal and a plastic container. Oftentimes, the welding step melts the plastic in the vicinity of the terminal so that upon cooling, the reformed plastic does not seal properly about the terminal. Given just the smallest crevice or space, the sulfuric acid will eventually find its way to the exterior of the battery case via the terminals. The leaking problem, as alluded to earlier, is exacerbated by the fact that most side terminal designs utilize a terminal construction which partially or completely passes through the sidewall. Accordingly, one way to alleviate the leaking problem has been the employment of wax about the back end of the terminal.
In summary, although sound in principle, injection molding techniques are relatively expensive when compared to the disclosed invention. Moreover, designs that employ plugs traversing the wall have been known to leak on occasion.